Neutron detection has a range of applications, including nuclear reactor monitoring, materials science research, nuclear material detection, and nuclear material forensics. Scintillators, materials that absorb energy from incoming radiation and emit photons when the scintillator returns to its original energy state, are used in one method of neutron detection. Conventional scintillators, which are generally inorganic crystals, are hygroscopic and require protection from atmospheric conditions to avoid degradation. Therefore, materials containing uranium oxide or actinide phosphate, such as, RbUPO4F2 and CsUPO4F2, have been considered promising as state-of-the-art scintillators because of their characteristic high density, optical clarity, and stability when exposed to atmospheric conditions. Yet, synthesis of single crystals of these new materials has, to date, been unsuccessful.
Moreover, certain uranium oxide or actinide phosphate crystals, particularly RbUPO4F2 and CsUPO4F2, have the potential to incorporate large quantities of radionuclides into their crystal structures. In-fact, it has been hypothesized that the structure of these two materials may lend itself to the replacement of the rubidium or cesium atomic sites with cesium-137 or strontium-90 radioisotopes. By incorporating these radioisotopes directly into the crystal structure, it is believed that resultant materials may be radiation-damage resistant solid to contain radioactive wastes without the threat of leaking or degradation over time. Again, as noted above, synthesis of these single crystals of actinide phosphate has, to date, been unsuccessful.
Conventional radioactive waste undergoes a vitrification process, which incorporates the waste into a glass structure. A borosilicate glass material is commonly used for this process, but is largely inadequate because of a lack of stability when exposed to radiation for extended periods. When the structure of the glass material become unstable, the glass structure is less effective in containing radioactive wastes. Some have hypothesized that phosphate structures of RbUPO4F2 and CsUPO4F2 have the potential to render such radioactive waste stable with regards to temperature and chemical exposure. Similarly, with the incorporation of the uranium in the structure, it also makes it extremely likely that these materials will be stable when exposed to radiation for extended periods. With a large amount of nuclear wastes produced each year by medical, industrial, and military processes, these materials would fill a large void that exists in current radioactive waste storage and disposal technology.
Finally, some uranium based single crystals may be useful as a nuclear fuel in a molten salt reactor process.
Uranium-based crystals may, therefore, be used for a plurality of reasons, not limited to those herein. Yet, to date, bulk substrate of single uranium-based crystals is difficult to achieve. This difficulty lies in that, traditionally, high temperatures (in excess of 1000° C.) are needed for crystal growth: that is, in excess of 3000° C. for a skull melting technique and in excess of 1000° C. for both flux growth and chemical vapor transport.
Thus, there remains a need for methods of growing single, bulk substrate of uranium-based crystals of high purity, significant size, and high quality.